Note: Descriptions are shown in the official language in which they were submitted.
1~14q27
BACKGROUND OF THE INVENTION:
The present invention relates to a composite~
substrate for a fuel cell of phosphoric acid type and a
process for producing the same. More in detail, the present
invention relates to a composite substrate provided with
two electrode substrates, a separator and (1) peripheral
sealers or (2) both the peripheral sealers and gas-distri-
butors (external manifold type), and a process for producing
the same. In addition, "electrode substratei' in the pre-
sent invention means all electrode substrates each of
which becomes an electrode for a fuel cell by only applying
a catalyst to the electrode substrate or only stacking on
the electrode substrate a porous electrode carrying a
catalyst which has been separately prepared.
In recent years, as an apparatus for generating
clean energy or a freely switchable generator which can
contribute to saving natural resources by a normalization
of the operation of thermal power generation or water-
power generation or an improvement of energy efficiency,
a fuel cell and development and utilization of a system
surrounding the fuel cell have been highly demanded.
Hitherto, as the fuel cell, a fuel cell of bipolar
separator type in whLch a bipolar separator obtained by
ribbing a gas-impermeable graphitio thin plate and a
porous and carbonaceous plate are used in combination have
been publicly known, however, contrary to the above-
~r
1 31 ~27
mentioned, a fuel cell of monopolar type formed by stackingan electrode substrate which has been provided with ri~bs
on one surface thereof and have a flat structure on the
another surface thereof, a catalyst layer, a matrix
impregnated wi~h an electrolyte and a separator sheet has
been developed. In the fuel cell of monopolar type, a
reactant gas (oxygen or hydrogen) diffuses from flow
channels for reactant gases formed by the ribs provided
on the electrode substrate to a flat surface of the elec-
trode.
Although such an electrode substrate is usually
made of a caxbonaceous material from the viewpoint of
physical properties such as heat-resistance~ corrosion-
resistance, electro-conductivity, mechanical strength,
etc. and the ease of retaining poxosity therein and the
electrode substrate is used by stacking them as has been
stated above, it is difficult to make top surfaces of the
ribs perfectly flat and therefore, the electric- and
thermaI contact resistance between the ribs and the
separator is too large to be disregarded.
Generally, it is said that the above-mentioned
contact resistance is larger than the transmission
resistance within the substrate by several times, and
such contact resistance causes conclusive defects such as
uneveness of distribution of the temperature between the
cells and reduction of an efficiency of electric generation. ;
1 3 1 ~
In order to solve the above-mentioned problem
of contact resistance, a composite substrate has been~
proposed wherein the electrode substrate, the separator,
etc. of the stacked structure of the above-mentioned
fuel cell have been adhered together by an adhesive and
integrated into one body of carhon by calcination thereof.
Although in such a composite substrate, the contact
resistance present on the contact surface can be made
zero by joining them into one body, since the composite
substrate is produced by adhering the carbonaceous
materials together and carbonizing and calcining the thus
adhered materials as has been stated, there are cases of
exfoliation of the adhered surfaces during the calcining
step due to a difference of rates of thermal expansion
and shrinkage between the carbonaceous materials and the
adhe,sive, and cases of causing warps, distortions or
cracks in the product. In such cases, the reduction of the
producti~e yield is caused, and accordingly, improvements
of the product and process have been desired.
As a result of the present inventors' studies
from the conception that the exfollation of the cOmpOSLte
substrate for a fuel cell in the calcining step (to a
maximum temperature of 3000C) is considered to be due to
the difference of the thermal expansion between the porous
and carbonaceous layer and the gas-impermeable layer
(separator) in the temperature-raising step or to the
4 --
.
131~q27
difference of shrinkage between the above-mentioned two
layers in the cooling step to room temperature after `
completing calcination and that the difference of thermal
expansion and shrinkage between the above-mentioned two
layers may be reduced or removed by a buffer layer pro-
vided between the two layers, it has been found by the
present inventors that the above-mentioned problem of
inter-layer exfoliation can be solved by inserting a -
flexible carbon sheet which has a relatively large rate
of thermal expansion and shrinkage, an adhesiveness to
the adhesive, etc. and a relatively low gas-permeability,
as a material for the buffer layer, between the above-
mentioned porous and carbonaceous layer and the separator
and joining the above-mentioned two layers via a carboni-
zable adhesive (for instance, refer to U.S. Patent No.
4,579,789).
However, in general, the substate as the electrode
in ~the fuel cell of phosphoric acid type is stacked 50
that one surface thereof contacts to the phosphoric acid
matrix and the another surfaces thereof faces to the
separator. Still more, in the case of stacking the elec-
trode substrate for obtaining a fuel cell, a sealer
.material is provided on the peripheral part thereof to
prevent diffusion of the reactant gas from the side of
the electrode substrate to outside thereof.
1 3 1 4'~27
Accordingly, particularly in the case where the
composite substrate is formed of the porous and carbo~a-
ceous electxode substrate up to the edge part thereof and
the flow channels of reactant gases open directly at the
edge part in the composite substrate of the external
manifold type, the peripheral sealer which is compact and
carbonaceous and the electrode substrate which is porous
and carbonaceous are disposed opposite each other across
the separator on the peripheral region of the separator,
and there has been a problem of causing a certain degree of
a warp or a strain in the joining part of the materials
due to the difference of the thermal shrinkage between
the mat~rials even by the intervention of the flexible
carbon sheet. As the means for preventing the above-
mentioned warp, the materials with an extrèmely small
difference of the thermal shrinkage should be selected,
and such a restriction has been the obstruction in the
production of the composite substrate.
Furthermore, as a problem poin~ of the conventional
fuel cell, the adhesion between the composite materials in
the fuel cell has been carried out by using a carbon
cement.
However~ since the carbon cement is eroded by
phosphoric acid, ~here has been a possibility that exfolia-
tion between the composite materials is caused and the
reactant gas leaks through the joined parts.
~ 3 ~ ~927
In addition, there has been another problem
in the point of mechanical strength of the electrode ~
substrate resulting in breaking on handling in the case
where the area of the substrate is too large, because
the electrode substrate is a thin plate.
Further, a method of joining porous electro-
conductive materials wherein the gas-impermeability
between the porous electroconductive materials has been
increased, has been proposed recently. According to the
proposed method, the porous electroconductive material is
impregnated with a fluorinated ethylenepropylene copolymer,
a polysulfone resin, etc., and the thus impregnated layer
is joined as an interface to another electroconductive
material by hot-pressing while maintaining electroconduc-
tivity through the gas-impervious region (for instance,
refer to U.S. Patent No. 4,505,992).
However, in the case of using the above-mentioned
methods for sealing periphery of a composite substrate
for a fuel cell, although the passage of~the gas between
the ~wo carbonaceous materials is prevented by the thus
resin-impregnated carbon layer, since the usable electro-
conductive material is limited to the porous carbonaceous
material and such a porous carbonaceous material is weak
in mechanical strength, the usage of the thus~obtained
composite material is limited.
.
-- 7 --
1 31 ~9~7
On the other hand, even in the case where an
electrode in a composite electrode substrate is produced
by the above-mentioned method, the thus obtained resin-
impregnated electrode is unsatisfactory in quali.ty for
using it in the composite electrode substrate for a fuel
cell, because the used thermoplastic resin is substantially
large in resistance to thermal and electric conductivities.
As a result of the present inventors' studies
for finding a process for producing a composite substrate
for a fuel cell, which does not have the above-mentioned
defects and is excellent in mechanical strength/ electrical
properties and chemical resistance, it has been found out
by the present inventors that the composite substrate
having the above-mentioned excellent properties can be
obtained in a high yield by joining a porous and carbona-
ceous electrode substrate provided~with~flow channels for
reactant gases and a gas-impermeable separator comprlsing~
a compact carbonaceous~material via a flexible carbon~sheet
and further joining (1) a peripheral sealer comprising a
gas-impermeable and compact carbon material or (2) both
the peripheral sealer and a gas-distributor comprising~
a compact carbon material to the above-mentioned separator
via a fluorocarbon resin layer, and on the basis of the ~:
above-mentioned flndings, the present inventors have
attained the present invention.
-- 8 --
t 3 1 4927
Namely, the first object of the present invention
is to provide a composite substrate provided with peripheral
sealers for a fuel cell, wherein the peripheral sealexs
have been joined to a separator and the these materials
have been integrated.
The second object of the present invention is to
provide a composite substrate provided with peripheral
sealers and gas-distributors (of the external manifold type)
for a fuel cell, wherein porous and carbonaceous electrode
substrates, peripheral sealers and gas-distributors have
been joined to a separator and the above-mentioned
materials have been integrated.
The third object of the pre:ent invention is to
provide a composite substrate for a fuel cell, which has
a structure that can prevent the generation of warps,
distortions or cracks at the time ~f producing the composite
substrate.
The fourth object of the present invention is
to provide a composite substrate ~or a fuel cell o~ a
phosphoric acid-type. ~
The fifth object of the present invention is to
provide a composite substrate for a fuel cell, which is
excellent in mechanical strength and handling properties
at the time of producing the composite substrate.
The other objects and the merits of the present
invention will be apparent to persons skilled in the art
.... ~.; ~
1~i14927
from the following detailed description of the present
invention.
SUMMARY OF THE INVENTION-
In a first aspect of the present invention, there
is provided a composite substrate for a fuel cell comprising
(l) a separator,
(2) two porous and carbonaceous electrode sub-
strates which are provided with a plurality of grooves
on one of surfaces thereof and have another flat surface,
each of the electrode substrates being joined
to the both surfaces of the separator via a flexible
carbon sheet so that the grooves form flow channels for
reactant gases and the flow channels in one of the elec-
trode substrates are perpendicular to those in the~another -
electrode substrate, the flexible carbon sheet being :
interposed only between the joining surfaces of..the
separator and tops of ribs forming the grooves of the
electrode substrate, and the sepa.rator having an extended
part beyond a periphery of the eIectrode substrate,~and
(3a) a:pair of peripheral sealers on the side of:
the electrode substrate parallel to the flow channels for
reactant gases therein, which comprise a gas-impermeable
and compact carbon material, or:
- 10 -
1 3 1 ~9~7
t3b) a pair of peripheral sealers on the side of
the electrode substrate parallel to the flow channels
for reactant gases therein, which comprise a gas-
impermeable and compact carbon material and a pair of
gas-distributor on the side of the electrode substrate
perpendicular to the flow channels for reactant gases
therein, which comprise a gas-impermeable and compact
carbon material and are provided with a passage for
distributing reactant gases,
(3a) the peripheral sealers or (3b) the peri-
pheral sealers and the gas-distributors being joined to the
extended part of the separator beyond the electrode
substrate, via a fluorocarbon resin layer.
In a second aspect of the present invention, there
is provided a process for producing a composite substrate :
for a fuel cell, comprising steps of
(1) adhering a flexible carbon sheet onto one surface
of each of two electrode substrate materials of a fl~at
plate-form without grooves and of the prescribed dimension
by an adhesive, ~ :
(2) providing grooves of a desired dimension for forming
flow channels of reactant gases on the joining:surface
side of each of the electrode substrate materials by cut-
processing,
- 11 -
~31~27
(3) joining a separator material to the surface of the
fle~ible carbon sheet remaining on the thus cut-processed
surface of each of the electrode substrate materials in
face to face,
(4) calcining the thus composed materials at a temperature
of not lower than about 800C under a reduced pressure
and/or in an inert atmosphere thereby producing a composite
body comprising the electrode substrates and the separator,
and
(5a) joining a pair of peripheral sealers comprising a
gas-impermeable and compact carbon material to an extended
part of the separator, which extends be~ond a periphery
of the electrode substrate parallel to the flow channels
for reactant gases therein, via a sheet or a dispersion
of fluorocarbon resin, or
(5b) joining a pair of peripheral~sealers comprlsing a
gas-impermeable and compact carbon material to an extended
part of the separator, which extends beyond a periphery
of the electrode substrate parallel to the flow channels
for reactant gases therein, via a sheet or a dispersion of
fluorocarbon resin and further joining a pair of gas-
distributors comprising a gas-impermeable and compact
carbon material and having grooves forming a passage for
distributing reactant gases to an e~tended part o~ the
separator, which extends beyond a periphery of the
electrode substrate perpendicular to the flow channels
- 12 -
131~7
for reactant gases therein, via a sheet or a dispersion
of fluorocarbon resin.
BRIEF EXPLANATION OF DRAWINGS:
of the attached drawings, Fig. 1 is an oblique
view of the composite substrate provlded with the peripheral
sealers according to the present invention and Figs. 2 and
3 are respectively the oblique views of the composite
substrate provided with the peripheral sealers and the
gas-distributors according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION:
The present invention rela-tes to a composite
substrate for a fuel cell comprising
(l) a separator,
(2) two porous and carbonaceous electrode
substrates which are provided with a plurality of grooves
on one of surfaces thereof and have another flat surface,
each of the electrode substrates being joined to
the both surfaces of the separator via a flexible carbon
sheet so that the grooves form flow channels for reactant
gases and the flow channels in one of the electrode
substrates are perpendicular to those in the another
electrode substrate, the flexible carbon sheet being
interposed only between the joining surfaces of the
separator and tops of ribs forming the grooves of the
- 13 -
1 31 ~927
electrode substrate, and the separator having an extended
part beyond a periphery oE the electrode substrate, and
(3a) a pair of peripheral sealers on the side
of the electrode substrate parallel to the flow channels
for reactant gases therein, which comprise a gas-impermeable
and compact carbon material, or
(3b) a pair of peripheral sealers on the side
of the el~ctrode substrate parallel to the flow channels
for reactant gases therein, which comprise a gas-
impermeable and compact carbon material and a palr of
gas-distributor on the side of the electrode substrate
perpendicular to the flow channels for reactant gases
therein, which comprise a gas-impermeable and compact
carbon material and are provided with a passage for ~:
reactant gases,
(3a) the peripheral sealecs or (3b) the peripheral
sealers and the gas-distributors being joined to the
extended part of the separator beyond the electrode
substrate, via a fluorocarbon resill layer. : :
: Still more, the present invention relates to a
process for producing:a composite substrats for a fuel
cell, comprising steps of
~l) adhering a flexible carbon sheet onto one surface
of each of two electrode substrate materials of a~flat
.
- 14 -
1 31 ~q27
plate-form without grooves and of the prescribed dimension
by an adhesive,
(2) providing grooves of a desired dimension for forming
flow channels of reactant gases on the joining surface
side of each of the electrode substrate materials by
cut-processing,
~3) joining a separator material to the surface of the
flexible carbon sheet remaining on the thus cut-processed
surface of each of the electrode substrate materials in
ace to face,
(4) calcining the thus composed materials at a temperature
of not lower than about 800C under a reduced pressure
and/or in an inert atmosphere thereby producing a composite
body comprising the electrode substrates and the separator,
and ~
(5a) joining a pair of peripheral sealers comprising a
gas-impermeable and compact carbon~material to an extended
part of the separator, whlch extends beyond a:periphery
of the electrode substrate parallel:to the flow c~annels
for reactant gases therein, via a sheet or~a dispersion
of fluorocarbon resin, or
(5b) joining a pair of peripheral sealers comprising a
gas-impermeable and compact carbon material to:an extended
part of the separator, which extends beyond a periphery of
the electrode substrate parallel to the flow channels for
reactant gases therein, via a sheet or a dispersion of
-- 15 --
1 3 1 ~927
fluorocarbon resin and ~urther joining a pair of gas-
distributors comprising a gas-impermeable and compact~
carbon material and having grooves forming a passage for
distributing reactant gases to an extended part of the
separator, which extends beyond a periphery of the elec-
trode substrate perpendicular to the flow channels for
reactant gases therein, via a sheet or a dispersion of
fluorocarbon resin.
Of the attached drawings, Fig. 1 is an oblique
view of a composite substrate provided with the peripheral
sealers according to the present invention. The composite
substrate of Fig. 1 has a construction comprising a
separator 1, two electrode substrates 2 which have grooves
forming flow channels 6 for reactant gases together with
the separator and are disposed on the both sides of the
separator and peripheral sealers 3 which are disposed
on the edge (namely, side) of the electrode substrate 2
in the parallel direction to the flow channels 6 for
reactant gases of the electrode substrate.
The surface area of the separator 1 is larger
than that of the electrode substrate 2, and the separator
1 has been extended beyond a periphery of the electrode
substrate which is parallel to the flow channels 6 for
reactant gases in each of the electrode subs~rates (the
outer edge of the extended part coincides with the outer
edge of the another electrode substrate). The peripheral
- 16 -
t; 3 1 ~.q27
sealer 3 has been joined to the above-men-tioned extended
part. Only between the joining surfaces of the separàtor
1 and tops of ribs forming the grooves of the electrode
substrate 2, a flexible carbon sheet 4 has been interposed,
and accordingly, the flow channels 6 for reactant gases
have been prescribed by the grooves of the electrode
substrate, the separator and the flexible carbon sheet.
The peripheral part of the separator, which has been
extended beyond the electrode substrate and the peripheral
sealer 3 have been joined via a fluorocarbon resin S.
Fig. 2 is an oblique view of a composite substrate
provided with peripheral sealers and gas-distributors
according to the present invention. Fig. 3 has been given
to show a construction of the composite substrate according
to the present invention and shows the same view as Fig. 2
except for inexistence of both (1) one of the gas-distri-
butors 7 having grooves forming passage 8 for distrlbuting
reactant gases, which will be explained later, and (2)
the fluorocarbon resin 5 on the part to which the gas-
distributor is ~oined.
In Figs. 2 and 3, the composite substrate
according to the present invention has a construction
comprising (1) the separator 1, (2) the two electrode
substrates 2 which have the grooves ~orming the flow
channels 6 for reactant gases together with the separator
and are provided on the both sides of the separator so
- 17 -
.
.
131~27
that the flow channels 6 in one of the electrode substrates
are perpendicular to those in the another electrode
substrates, (3) the peripheral sealers 3 which have been
disposed on the edge (namely/ side) of the electrode
substrate and (4) the gas-distributors 7.
The surface area of the separator 1 is larger than
that of the electrode substrate 2 and as is seen in Figs.
2 and 3, the separator has been extended beyond a periphery
of the electrode substrate, and the peripheral sealer 3
and the gas-distributor 7 have been joined to the above-
mentioned extended part (the outer edge of the extended
part of the separator coincides with the outer edge of
the peripheral sealer and the gas-distributor after joining).
The gas-distributor 7, which is joined to the
extended part of the above-mentioned separator beyond the
periphery of the electrode substrate perpendicular to the
10w channel 6 for reactant gases therein, has grooves
forming a flow passage 8 for distributing reactant gases
together with the separa~or, and the peripheral sealer 3,
which is joined to the extended part of the separator
beyond the periphery of the electrode substrate parallel
to the flow channel 6 therein, does not have the above~
mentioned grooves. Although the grooves in the gas-
distributor 7 form the flow passage 8 for distributing
reactant gases for the supply of the reactant gases from
outside, it is not particularly necessary that the shape
- 18 -
.
13~4~27
of the cross-section thereof coincides with that of the
flow channel 6 for reactant gases, and further, it is~not
necessary that all of the openings of the flow channels 6
open to the flow passage 8 for distributing reactant
gases. Namely, the cross-sectional shape of the grooves
of the gas-~istributor 7 may be selected so as to be
sufficient for maintaining the flow volume of the gases
necessary for operating the fuel cell provided with the
composite substrate.
Between the separator 1 and the electrode substrate
2, a flexible carbon sheet 4 has been interposed. Still
more, in E'igs. 2 and 3, the flexible carbon sheet 4 has
been interposed only between the joining surfaces of the
separator 1 and tops of the ribs of the electrode substrate
2, and accordingly, the flow channel 6 for reactant gases
have been prescribed by the grooves of the electrode
substrate, the separator and the flexible carbon sheet, and
the flow passage 8 for distributing reactant gases has a
shape prescribed by the grooves of the gas-distributor
7 r the separator 1 and the fluorocarbon resin 5.
In the production of the composite substrate of
Figs. 2 and 3, the flexible carbon sheet 4 may be joined
to the whole area of the separator facing to the electrode
substrate (except for the surface area on which the
peripheral sealer and the gas-distributor are joined vla
a fluorocarbon resin layer) so that the size of the flexible
-- 19 --
1; 3 1 ~7
carbon sheet is the same as that of the electrode substrate
(such a situation has not been illustrated hereinJ. However,
from the viewpoint of the thickness of the composite
substrate, since the former structure can make the thickness
of the composite substrate thinner than that of the latter
structure by the thickness of the flexible carbon sheet
while retaining the same cross-sectional area of the flow
channels for reactant gases, the former structure is
preferable.
In Figs. 2 and 3, the peripheral part (extended
part) of the separator beyond the electrode substratej the
peripheral sealer 3 and the gas-distributor 7 have been
respectively joined via the fluorocarbon resin 5. Although
the fluorocarbon resin may be interposed between the
joining surface of the peripheral sealer and:the gas-
distributor both of which are joined to the same side of
the separator, it is not particularly necessary, because
the gas-leakage does not become any problem:in the case
where the product is used in combination with the external
mani~old which is made so as to cover the above-mentioned
joining part.
Still more in the composite substrate of Figs. 1
to 3, the separator 1, the:flexible carbon sheet 4 and
the electrode substrate 2 have been made into one body by
- 20 -
1 3 1 ~927
carbonization and calcina-tion.
The electrode substrate used according to thè
present invention is a porous and carbonaceous material
and preferably having the following specific properties,
and also an electrode substrate material (namely, a
material for the porous and carbonaceous electrode substrate)
used in the present invention has preferably the same
following specific properties after calcining the material
at a temperature of not lower than 800C under a reduced
pressure and/or in an inert atmosphere. That is,
Mean bulk density of from 0.3 to 0.9 gjcc,
Gas-permeability of not less than 200 ml/cm2.hour-
mmAq and
Electric resistivity of not more than 200 mQ-cm.
The separator used according to the present
invention pre~erably has the following specific properties:
Mean bulk density of not less than 1.4 gjcc,
Gas-permeability of not more than ~10 6~ml/cm2
houI 'IrlInAq, ` ~
Electric resistivity o~ not more than 10 mQ~cm and
Thickness of not more than 2 mm.
The material of the peripheral sealer and the~
gas-distributor used in the composite substrate according
to the present inventlon is preferably a compact carbon
material of the following properties:
- 21 -
1 31 ~27
Mean bulk density of not less than 1.40 g/cc,
Gas-permeability of not more than 10 4 ml/cm2~.
hour-mn~q and
Difference of the thermal expansion coefficient
thereof from that of the separator material is not more
than 2 x 10 6/oC.
Particularly, the above-mentioned material is
preferably a material subjected to calcination at a
temperature of not lower than 800C under a reduced pres-
sure and/or in an inert atmosphere.
As has been already described, in the composite
substrate for a fuel cell accord:ng to the present
invention, all of the peripheral sealers, all of the
gas-distributors and the separator have been joined
respectively ~ia a fluorocarbon re~in. Although an
amount of gas leakage through the per~ipheral sealers
including the joined parts~is controlled mainly by
diffusion and is not so much influenced by the pressure~
.
the amount of gas leakage is preferably not more than
10 2 ml/cm-hour.mmAq in the case where the amount of gas
leakage per unit time per unit length of the pariphery
of the joining part under a differential pressure~of
500 mmAq. is represented by the relationship of
[the amount of gas leakage/(side~length of periphery~-
tdifferential pressure)].
- 22 -
~ 3 1 ~ 7
The ~luorocarbon resin used according to the
present invention is a fluorocarbon resin of a melting
point of not lower than 200C and is not particularly
limited, however, for instance, a tetrafluoroethylene
resin (an abbreviation of PTFE, a melting point of
327C, a thermal deformin~ temperature of 121C under
4.6 kgf/cm2G.), a copolymer resin of tetrafluoroethylene
and hexafluoropropylene (an abbreviation of FEP, a melting
point of from 250 to 280C, a thermal deforming temperature
of 72C under 4.6 kgf/cm G.), a fluoroalkoxyethylene resin
(an abbreviation of PFA, a melting point of from 300 to
310C, a thermal deformation temperature of 75C under
4.6 kgf/cm2G.) and a fluorinated copolymer resin of
ethylene and propylene (an abbreviation of TFP, a melting
point of from 290 to 300C) may be exemplified. The above-
mentioned fluorocarbon resins are c:ommercialized.
Of the above-mentioned fluorocarbon resins,
tetrafluoroethylene resin is preferably used particularly
in the present invention and is commercialized under the
trade name of TEFLO ~.
In the present invention, the above-mentioned
fluorocarbon resin is used as, for instance, a sheet of
about 50 ~m in thickness or a dispersion containing about
60% by weight of the resin. Into the dispersion, a small
amount of a surfactant may be added.
As the electrode substrate material (namely, the
- 23 -
1~14~27
material for the porous and carbonaceous electrode
substrate) used according to the present invention, the
following materials may be mentioned:
(1) A material made by molding a mixture of
short carbon fibers, a binder and an organic granular
substance by heating under a pressure (for instance,
refer to Canadian Patent No. 1,205,857). Particularly,
the material obtained by molding a mixture of from 20 to
60~ by weight of short carbon fibers of not more than~2 mm
in length, from 20 to 50% by weight of a phenol resin
and from 20 to 50% by weight of an organic granular
substance (a pore regulator) at a molding temperature of
from 100 to 180C, under a molding pressure of from 2 to~
100 kgf/cm G. for from l to 60 min~ and
(2) A material obtained by calcining the material
shown in the above (1) at a temperature of not lower than
800C under a reduced pressure and/or in an inert atmosphere.
As a separator material (namely, the material
for the separator) used according to the present invention,
a compact carbon plate which shows a rate of calcining~
shrinkage of nct more than 0.2 % in the case where the
material is calcined at 2000C under a reduced pressure
and/or in an inert atmosphere is desirable. The separator
material is usually in a flat plate form, and the area of
one of the surfaces thereof is usually larger than that
of the flat part of the electrode substrate material.
- 24 -
1314'~27
However, as will be described later, in the step of
joining the separator material and the electrode substrate
material, the surface area of the former may be the same
as that of the latter.
As the flexible carbon sheet used for joining
the electrode substrate material and the separator material
in the composite substrate according to the present
invention, a flexible graphite sheet of not more than 1 mm
in thickness which has been prepared by compressing the
expanded graphite particles obtained by subjecting graphite
particles of not more than 5 mm in diameter to acid-
treatment and further heating the thus acid-treated
particles, shows a bulk density of 1.0 to 1.5 g/cc and
a rate of compression strain (namely, the rate of strain
to the compression load of 1 kgf/cm2G.) of not more than
0.35 x 10 2 cm2/kgf and has a flexLbility that the sheet
is not broken in the case of bending the sheet to 20 mm
in the radius of curvature is preferable, and~of the
commercialized flexible graphite sheets, GRAFOIL~made
by U~C.C. is a suitable example.
The:flexible carbon sheet used also according
to the present invention is produced by mlxing carbon
fibers of not less than 1 mm in mean length whlch fibers
have been thermally treated at a temperature of preferably
not lower than l,000C, more preferably not lower than
1,500C under a reduced pressure and/or in an inert
- 25 -
~3~4~27
atmosphere, with a binder of not less than 10~ in the
carbonizing yield, for instance, pouring the above binder
into the matrix of the above carbon fibers, molding the
thus composite materials by heating under a ~ressure and
calcining and carbonizing the thus molded material at a
temperature of not lower than 850C under a reduced
pressure and/or in an inert atmosphere. The thus produced
flexible carbon sheet has a thickness of no-t more than
1 mm, a bulk density of 0.2 to 1.3 g/cc and a rate of
compression strain of not more than 2.0 x 10 1 cm~/kgf,
wherein the carbon lumps derived from the above-mentioned
binder have been dispersed in the matrix of the carbon
fibers and restrain a plurality of the carbon fibers and
by the carbon lumps the carbon fibers are slidably held
to one another. The just-mentioned flexible carbon sheet
has a flexibility of not being broken in the case of bending
the sheet to 10 mm in the radius o~ curvature.
As the adhesive used on each of the joining surfaces
in the case of joining the above~mentioned electrode substrate
material to the separator material via the flexible carbon
sheet, any adhesive usually used in joining carbon materials
may be used, however, it is desirable that the adhesive is
a thermosetting resin selected from the group consisting `
of phenol resins, epoxy resins and furan resins.
Although the thickness of the layer of the above-
mentioned adhesive is not particularly limited, it is
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131~927
desirable to apply the adhesive thereupon uniformly in
the thickness of usually not more than 0.5 mm.
In addition, the joining by the above-mentioned
adhesive can be carried out at a temperature or from 100
to 180~C under a press-pressure of from 1 to 50 kgf/cm2G.
for a press time of from 1 to 120 min.
After joining the electrode substrate material and
the flexible carbon sheet while using the above-mentioned
adhesive under the above-mentioned joining conditions,
the grooves forming the flow channels for reactant gases
are made by cut-processing in the desired dimensions on the
surace to which the carbon sheet has been adhered. The
cut-processing can be carried out in the optional means, ~
for instance, carried out by using a diamond blade.
After applying the adhesive on the suraces of
the 1exible carbon sheets remaining on a pair of the
electrode substrate materials to which the cut-processing
have been finished, and joining the adhesive surfaces to
the both surfaces of the separator so that the flow
channels or reactant gases in one of the electrode substrate
materials are perpendicular to those in the another elec-
trode substrate material, as in the above-mentioned case
of joining the electrode substrate materials and the
- 27 -
,
1 31 4927
flexible carbon sheet, the thus joined materials are
calcined at a temperature of not lower than 800C under
a reduced pressure and/or in an inert atmosphere to produce
a composite body comprising the electrode substrates and
the separator.
Further, after joining the electrode substrate
material and the flexible carbon sheet, the calcination
thereof may be carried out under the same condition before
subjecting the joined material to the cut-processing,
namely the calcination is carried out two times, thereby
ensuring the carbonization of the materials.
After joining the electrode substrate material
and the separator material and calcining the thus joined
materials in the case where the electrode substrate and the
separator are of the same dimension (namely, the extended
part of the separator beyond the electrode substrate is
not provided thereupon), parts of the electrode substrate
and the flexible carbon sheet facing to the extended part
of the separator to be joined later are removed by
cutting, thereby exposing the joining surface (the ex-
tended part beyond the electrode substrate) of the separator
to be joined to the peripheral sealer and the gas-distri-
butor. Then, the thus exposed or previously provided
- 28 -
1314927
extended part of the separator is used for the junction.
Namely, after interposing a sheet of fluorocarbon
resi.n or applying a dispersion of fluorocarbon resin (1)
between (i) the extended part (which is the joining surface
to the peripheral sealer and extends beyond the periphery
of the electrode substrate parallel to the flow channels
for reactant gases) and (ii) the surface of the peripheral
sealer to be joined thereto, or (2) between (i) the
extended part (which is the joining surface to the peri-
pheral sealer and extends beyond the periphery of the
electrode substrate parallel to the flow channels for
reactant gases) and (ii) the surface of the peripheral
sealer to be joined thereto and between (i) the extanded
part of the separator (which is the joining surface to
the gas-distributor and extends beyond the periphery of
the electrode substrate parpendicular to the flow channels
for reactant gases) and (ii) the surface of the gas-
distributor to be joined thereto, the thus treated materials
are press-joined by melt-adhesion at:a temperature of not
lower than the temperature of lower than the melting point
of the fluorocarbon resin by 50C under a pressure of not
less than 1 kgf/cm2G.
The grooves of the gas-distributor may be preli-
- 29 -
1 31 ~927
minarily made by cut-processing in the desired dimenslons
by an optional method as in the case of making the grooves
on the above-mentioned porous and carbonaceous electrode
substrateO
Further, the fluorocarbon resin may be prelimi-
narily applied by melt-adhesion to the peripheral sealer or -
the peripheral sealer and the gas-distributor.
In order to obtain the construction of the compo-
site substrate wherein the flexible carbon sheet has been
interposed only between the top surfaces of the ribs of
the electrode substrate and the separator aacording to the
present invention, various different methods can be~utilized.
For instance, after forming the groove by cut-processing
the electrode substrate material, the flexible carbon sheet
is joined only to the top surface of the thus formed rib,
etc. However, it is the most practical method that after
adhering the flexible carbon sheet to the not-yet cut-
processed electrode substrate material, the cut-processing
is carried out.
Since in the CQmpoSite substrate provided with the
peripheral sealer or the peripheral sealer and the gas-
distributor (external manifold type) for a fuel cell
according to the present invention, which is obtained as
- 30 -
.
1 31 ~q27
above, the periphera] sealer has been joined to the compo-
site substrate and formed in one body, the thus composite
substrate is excellent in preventing gas-leakage, and it is
not necessary, of course, to provide any peripheral sealer
for preventing the leakage of reactant gases on the side
of the fuel cell. Moreover, the composlte substrate
according to the present invention exhibits the following
effect.
Namely, since the electrode substrate and the
separator have been joined by the flexible carbon sheet into
one body and the peripheral sealer or the peripheral sealer
and the gas-distributor and the separator have been
joined by the fluorocarbon resin into one body, respectively,
the composite substrate according to the present invention
is excellent ln resistance to phosphoric acid and is
particularly useful as the composite electrode substrate
for a fuel cell of phosphoric acid type.
Moreover, in the composite substrate provided
with the peripheral sealer according to the present invention,
since the peripheral sealers have been disposed and joined
evenly on the both sides of the separator while holding
the separator alternately in both sides, such a structure
has a reinforcing e~fect and is excellent in handling
property at the time of producing the~fuel cell.
Furthermore, in the composite substrate provided
with the peripheral sealer and the gas-distributor according
- 31 -
~t~7
to the present invention, the peripheral sealer and the
gas-distributor both of which have been made of the same
material are opposite to each other across the separator
and accordingly, the thermal expansion coefficient of the
upper layer coincides with that of the lower layer. As a
result, the thermal stress between the separator and the
peripheral sealer becomes equal to that between the
separator and the gas-distributor, thus resulting in the
reduction of the warps and the distortion at the time of
producing the composite substrate in addition to the effect
obtained by interposing the flexible carbon sheet between
the joining surface of the electrode substrate and the
separator. -
Still more, since in the peripheral region of the
thin plate-like composite substrate,the peripheral sealer
and the gas-distributor have been disposed and joined in
face to face on the both sides of the separator while
holding the separator, such a structure has a reinforcing
effect and is excellent in the handling property at the
time o~ producing the fuel cell.
Moreover, in the composite substrate according to
the present invention, wherein the flexible carbon sheet
is interposed only between the top surfaces of the ribs
of the electrode substrate and the joining surface of the
separator, the thickness of the flexible carbon sheet
can be utilized as the effective height in the ribs of
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13~927
the electrode substrate. Namely, in comparison to the
composite substrate wherein the flexible carbon sheet~has
been disposed on the whole area of the separator facing
to the composite substrate, the thickness per one piece
of the electrode substrate of from 3.8 to 4 mm may be
reduced by from 0.3 to 0.5 mm, that is, from 7 to 13~
without any reduction of the cross section area of the
flow channel or reactant gases therein.
The present invention will be explained more in
detail while referring to the following non-limitative
examples.
EXAMPLE 1:
(1) Electrode substrate material:
Two pieces of the porous and carbonaceous flat
plate material preliminarily calcined at a temperature of
not lower than 800C ~made by KUREHA KAGAKU KOGYO Co., Ltd.,
under the trade name of KES-400, 650 mm in length, 690 mm
in width and 1.47 mm in thickness) were used as the elec-
trode substrate material.
(2) The separator material:
A piece of the compact carbon plate (made by
SHOWA DENKO Co., Ltd., under the trade name of SG-2, 0.6 mm
in thickness) was cut into 690 mm both in length and width
to prepare the separator material.
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1314927
(3) Peripheral sealers:
A piece of the compact carbon plate (made by~
TOKAI Carbon Co., Ltd., 1.~5 g/cc in bulk density and
1.5 mm in thickness) was cut into 4 pieces (each 690 mm
in length and 20 mm in width) to prepare the peripheral
sealers.
(4) Fluorocarbon resin:
A piece of TEFLO ~ sheet (made by NICHIAS Co.,
Ltd., 0.05 mm in ~hickness) was cut into 4 pieces according
to the dimensions of the peripheral sealer and the pieces
were used for the purpose.
(5) Flexible carbon sheet:
A piece of GRAFOIL~ (made by U.C.C., 1.10 g/cc
in bulk density and 0.13 mm in thickness) was suitably
cùt into 2 pieces according to the dimension of the
joining surface.
After applying an adhesive of phenol resin series
on each one side of the two electrode substrate ma~erials
and on one side of GRAFOIL~,the thus applied adhesive wa~s
dried. Then, the electrode substrate material and GRAFOIL~9
were joined respectively under conditions of 140C,
10 k~f/cm2G. and 20 min. of pressure-holding time.
Then, a plurality of grooves having a rectangular
cross section of 2 mm in width and 1 mm ln depth were
prepared in parallel to each other at intervals of 4 mm
on the GRAFOIL~-applied surface of each of the two sets
- 3~ -
1 ~ 1 4927
of the thus joined electrode subs-trate materials by cut-
processing with a diamond blade.
Thereafter, on the GR~FOIL~surface remaining on
the top of the rib forming the groove of the thus pro-
cessed body, the above-mentioned adhesive was applied
and dried.
In the same manner as above, the above-mentioned
adhesive was applied on the surfaces of the separator
material, and dried. Thereafter, the respective remaining
GRAE'OIL~ surfaces of the two electrode substrate materials
were joined to the both surfaces of the separator material
so that the plurality of the mutually parallel grooves
of one of the electrode substrate materials are perpendi-
cular to those of the another electrode substrate material,~
under the conditions of 140C in joining temperature,
10 kgf/cm2G. in joining pressure and 20 min. in pressure-
holding time. Then, the thus joined materials were
calcined at 2000C under a reduced pressure of 5 Torr and~
in gaseous nitrogen.
After calcination of the joined materials, the
part of the electrode substrate facing to the extended
part of the separator to be joined to the peripheral
sealer was cut off to expose the joining surface (extended
part) of the separator to be joined to the peripheral
sealer, and the TEFLO ~ sheet was lnterposed between the
joining surfaces of the peripheral sealer and the separator.
- 35 -
1 3 1 4927
Thereafter, the two materials were press-joined by melt-
adhesion of the resin at 350C under a pressure of 20`kgf/
cm G. and the pressure-holding time of 20 min.
According to the above-mentioned procedures, a
composite substrate of 3.8 mm in thickness was obtained.
In order to measure the adhesive strength of the
melt-adhered and press-joined surface of the thus obtained
composite substrate, a test piece taken from the product
was joined to the measuring jig by an adhesive of epoxy
resin, and the test piece was subjected to a tensile test.
Since the exfoliation was not caused at the joined part
of the TEFLO ~ sheet and was caused at the joined part of
the adhesive of epoxy resin, the adhesive strength was
presumed to be not less than 90 kgf/cm2. B~ the above-
mentioned test result, it can be said that the composite
substrate obtained as above can sufficiently stand for the
practical use as the composite substrate for a fuel cell.
EXAMPLE 2:
A composite substrate was prepared in the similar
manner as in Example 1 only except for using the following
flexible carbon sheet instead of GR~FOIL~ sheet used in
Example 1.
Namely, after~dispersing 7 parts by weiyht of
carbon fibers (made by KUREHA KAGAKU KOGYO Co., Ltd. by;
calcining isotropic pitch fihers at 2000C, under the trade
name of C 206S, 6 mm in length and 14 to 16 ~m in diameter)~
:
- 36 -
::
1 31 4927
and l part by weight of polyvinyl alcohol fibers (made
by KURARE Co., I,td. under the registered trada name of
KURARE VINYLO~ VBP 105-2, 3 mm in length) into water
and manufacturing into paper sheets by using an ordinary
paper machine, the thus manufactured carbon paper sheet
was dried, and the thus dried carbon paper sheet was
impreynated with a methanolic 20% solution of a phenol
resin. After removing the solvent from the thus impregna-
ted carbon paper sheet by drying~ the carbon paper sheet
was thermally shaped in a metal mold at 130C under a
pressure of lO kgf/cm2G. for 20 min. and then the thus
shaped paper sheet was calcined at 2000C under a reduced
pressure of 5 Torr and in gaseous nitrogen to obtain a
thin plate-like sheet of 0.3 mm in thickness. The thus
obtained sheet was 0.4 g/cc in bul~ density~ 8 x lO 2 cm2/kgf
in rate of compression strain and 5. 3 mm in flexibility
represented by radius of curvature. As in the case of
Example l, the sheet was suitably cut into two pieces,
each of them having the dimension corresponding to the
dimension of the joining surface with the electrode
substrate material.
By using the thus prepared flexible carbon sheet
instead of the GRAFOIL~ sheet in Example l, it was ~oined
to the electrode substrate material under the conditions
of 130C, lO kgf/cm2G. and 20 min. of the pressure-holding
time.
-- 37 --
1 31 ~q27
Thereafter, as in the case of Example 1, after
carrying out (1) preparing the groove by cut-processing
the surface of the flexible carbon sheet adhered to each
of the electrode substrate material, (2) press-joining
the electrode substrate materials to the both surfaces of
the separator material by heating by a pressure, (3)
calcining the composed materials and (4) cutting and
removing the part of the carbon sheet and the electrode
substrate facing to the extended part OL the separator to
be joined.to the peripheral sealer, the peripheral sealer
and the separator were press-j.oined by melt-adhesion of
the resin to obtain a composite substrate of 4.14 mm in
thickness for a fuel cell. .:
However, the conditions in joining thè separator
material and the electrode substrate material were 130C,
10 kgf/cm2G. and 120 min. of the p:ressure-holding:time.
: .. The thus obtained composite substrate was strong
in adhesive strength as that in Example 1 and could be
used actually. : ~ :
EXAMPLE 3
The following three kinds~of the composite ~
substrates mutually different~ln size were produced by
using the following materials.~
(1) Electrode_substrate~material:
The same material as that used in Example 1 as-
the electrode substrate material was cut into three pairs
- 38 -
1314927
of square pieces respectively having the length of one
side of 100, 300 and 600 mm, and each pair pieces of the
same size were used as the electrode substrate material.
The thermal expansion coefficient of these materials up
to 400C was 2.5 x 10 6/oC on the average.
(2) Sepaxator material:
A compact carbon plate (made by SHOWA DENKO Co.,
Ltd. of 0.6 mm in thickness) was cut into three square
pieces having respectively the length of the side of 100,
300 and 600 mm to obtain the respective separator materials,
the thermal expansion coefficient thereof being 3.0 x
10 /C.
(3) Peripheral sealer and gas-distributor:
.
A compact carbon plate (made by TOKAI Carbon Co.,
Ltd. of 1.85 g/cc in bulk density and 1.5 mm in thickness)
was cut into 6 groups of pieces respectively having the
length and width of 100 mm x 20 mm, 60 mm x 20 mm, 300 mm
x 20 mm, 260 mm x 20 mm, 600 mm x 20 mm and 560 mm x 20~mm,
one group consisting of four pieces, and these pieces were
used as the peripheral sealer and the gas-distributor.
On the pleces having shorter length (namel~, 60 mm,
260 mm and 560 mm, respectively) used as the gas-distri-
butor, after melt-adhering a TE~LO ~ sheet thereto, the
grooves of 8 mm in width and 0.6 mm in depth were provided
parallel to aach other with an interval of 12 mm by cut-
processing. The thermal expansion coefficient of these
- 39 -
1 31 ~927
all pieces was 2.5 x 13 6/oC.
(4) Fluoro arbon resin:
A TEFLO ~ sheet (made by NICHIAS Co., Ltd.,
0.05 mm in thickness) was cut into 4 pieces in accordance
to the size of the peripheral sealer, and the pieces were
used as the fluorocarbon resin.
(5) Flexible carbon sheet:
A GRAFOIL6~ (made by U.C.C., 1.10 g/cc in bulk
density and 0.13 mm in thickness) was suitabiy cut into
pieces in accordance to the size of the joining surface,
and each two of them were used as the flexible carbon
sheet.
After applying an adhesive of phenol resin series
onto one of the surfaces of each of the two electrode
substrate materials and one of the two surfaces of the
GRAFOII.~ and drying the thus applied adhesive, the elec-
trode substrate materials and the GRAFOIL~ were joined
together under the conditions of~l40C, 10 kgf/cm2G. and
20 min. of the pressure-holding time.
In the next place, a plurality of grooves of 2 mm
in width and 1 mm in depth parallel to each other and having~
a rectangular cross section were prepared at an interval
of 4 mm on the surface of GRAFOIL~ sheet adhered to each
of the two electrode substrate materials by cut-processing
while using a diamond blade.
::
- 40 -
1 31 4927
Thereafter, the ahove-mentioned adhesive was
applied on the remaining GRAFOIL~ surface of the thus~
processed body and dried.
Then, the respective remaining GRAFOIL~ surfaces
of the two electrode substrate materials were joined to
the both surfaces of the separator material so that the
plurality of the parallel grooves in one of the elec-
trode substrate materials are perpendicular to those in
the another electrode substrate material, under the joining
conditions of 140C, 10 kgf/cm2G~ and 20 min. of the pres-
sure-holding time, and the thus composed materials were
calcined at 2000C under a reduced pressure of 5;Torr and
in gaseous nitrogen.
After calcination, a part of the electrode
substrate and the GRAFOIL~ facing to the~extended part of
the separator to be joined to the peripheral sealer and
the gas-distributor was removed by cutting to expose
the joining surface of the saparator to be joined to the~
peripheral sealer and the gas-distributor, and a TEFLO
sheet was interposed between the ]oining surfaces of the
peripheral sealer and the extended par~t of;the separator.;~
In addition, the gas-distributor to wh1ch ;a TEFLO ~ sheet
had been preliminarily melt-adhered was piled while facing
the TEFLO ~ sheet surface to the surface of the separator.
Thereafter, the thus composed materials were press-joined
by melt-adhesion~under the conditions of 350C, 20~ kgf/cm2G.
- 41 -
1 3~ 4927
and 20 min. of the pressure-holding time.
By the above-mentioned procedures, three kinas
of the composite substrate provided with the peripheral
sealer and the gas-distributor for a fuel cell according
to the present invention were obtained. The length of the
side of the thus obtained products was respectively 100 mm,
300 mm or 600 mm, and the thickness thereof was 3.8 mm.
In the thus obtained composite substrate, the
difference of the thermal expansion coefficient between the
separator and the peripheral sealer and between the separa-
tor and the gas-distributor was 0.5 x 10 6joC, respectively.
The results of measuring the extent of the warp
of each of the thus obtained composite substrate were as
follows:
.
Length of the side
of the composite 100 300 600
substrate (mm)
~ _ ~ :
Warp (mm) 0 ~ 0.03 _0.05
: :
In addition, on measuring the adhesive strength
of the melt-adhered surfaces under a pressure in tbe sam~
manner as in Example l, the same results as in Example 1
were obtained and according to the results, the adhesive
strength was presumed to be not less than 90 kgf/cm2.
- 42 -
131'-Iq27
According to the above-mentioned measurements, it
can be said that -the thus obtained composite suhstrate
provided with the peripheral sealer and the gas-distributor
for a fuel cell could be put to practical use sufficiently.
:,
.,
- 43 -
